We are proposing to use a novel device to track foot bone motion in feet that are surgical candidates for foot reconstructive procedures. We aim to evaluate feet pre-surgery to explore subtle functional differences, and then again 1 year post-surgery to determine if the feet have been restored to normal. Feet come in a wide range of sizes and shapes, and often arch height (low or high) is the most common descriptor. Some feet which are nominally classified as low or high arched are actually just part of normal variation and are not of interest to this study. Rathe, we aim to examine symptomatic (painful) feet that have aberrant shapes and are candidates for surgery. Pes planus (low arch) is the most common foot condition in Americans; treatment is not well-standardized and may involve conservative or surgical options. There is little agreement among surgeons as to which procedures to perform, but an important consideration is the presence of hindfoot valgus. Without this deformity, painful flatfeet can often be corrected with medial column procedures, but if hindfoot valgus is present, then a calcaneal osteotomy is required. Pes cavus (high arch) is also prevalent in the US and among patients seeking surgical remedy, there is a key separator that divides pes cavus patients into two subgroups; these feet are either flexible and forefoot driven, with a plantar flexed first metatarsal and a correctible hindfoot varus, or they are fixed, with a rigid deformity. The former is often correctible with sof tissue procedures, while the latter requires an osteotomy of the first metatarsal and/or the calcaneus. The general concept in all these cases is to restore the load path through the foot to the ground. Studying foot bone motion and plantar pressure is a direct means of evaluating this, both within foot type group pre-surgically and compared to neutrally aligned subjects post-surgically. While plantar pressure measurement technologies are well established, quantifying foot bone motion in vivo is a non-trivial task. Despite great strides in recent decades in motion capture and medical imaging, these techniques remain fraught with problems when applied to the foot. For instance, motion capture requires multiple markers on the same bone, which due to the many small and intricately shaped bones in the foot necessitates grouping bones together. The technique also suffers from soft tissue motion artifact. Other methods, such as computer tomography (CT) or magnetic resonance imaging (MRI) have long scan times that preclude dynamic data collection. Until recently, the gold standards for motion analysis, including markers mounted via bone pins and dynamic radiostereometric analysis of tantalum beads, were highly invasive. Recently, biplane fluoroscopy has become an alternative to traditional retro-reflective systems or to the non-traditional but highly invasive systems. However, the foot provides some unique challenges to this technique, mostly due to the small, overlapping nature of the foot bones. Our group has developed a biplane fluoroscope system that is tailored to address the unique issues of the foot. The purpose of this study is to use our biplane fluoroscope to quantify foot bone motion of pes planus and pes cavus subjects pre- and post-surgery. We will compare and contrast these feet to a group of neutrally- aligned subjects to see how the pre- and post-surgical feet differ. Our Specific Aims are: [1] Refine our existing biplane fluoroscopy system. To decrease processing time, we will move from a central processing unit (CPU)-based to a graphics processing unit (GPU)-based software structure. We will also improve our calibration with enhanced three-dimensional (3D) localizer and distortion correction frames; [2] Compare the foot bone motion and plantar pressure of pes cavus, pes planus, and neutrally aligned subjects. Pre- surgically, we will study four groups of patients: 1) pes planus without hindfoot valgus, 2) pes planus with hindfoot valgus, 3) flexible pes cavus and 4) fixed pes cavus. We will study the same four groups 1-year post- surgery, as well as a control group of neutrally aligned patients. We will compare patients within foot type, between foot type and pre-/post-surgically. All groups will be compared to the neutrally aligned controls.